This shared instrumentation grant program proposal requests funds for the purchase of a state-of-the-art isothermal titration microcalorimeter (ITC). Calorimetry provides a wealth of information about macromolecular interactions and enzymatic kinetics by measuring the heats of reaction. This technique has distinct advantages over others, including that it can obtain information about the binding affinity, enthalpy and entropy of reaction and stoichiometry of the reaction in a single experiment and that it does not require the labeling of either the titrant or titrate molecules. Recent advances in instrumentation also allow for 10-fold lower sample amounts to be used per experiment and significantly decreased run time as compared to previous generation instruments. These considerations make this technique accessible to a broader spectrum of users and facilitates overall higher throughput, which are important features for shared instrumentation. Acquisition of the proposed MicroCal iTC200 would facilitate research programs directly related to human health issues in a number of important ways. Major users of this instrument propose to use this instrument to investigate the regulatory mechanisms of kinases involved in a variety of key cellular signal transduction pathways in humans (Prof. Natalie Ahn), RNA-based regulatory elements that directly sense cellular metabolites (Prof. Robert Batey), a nucleic acid aptamer that is an FDA- approved drug to fight macular degeneration (Prof. Arthur Pardi), and the nature of protein-DNA interactions at the end of linear chromosomes (Prof. Deborah Wuttke). These research goals along with those of the minor users emphasizes the strength of biophysics and biochemistry at the University of Colorado, Boulder and the proposed instrument would fulfill a core need of a large community of users.